1. Field of the Invention
The present invention relates to a self-checking circuit for accurately detecting a component having an error in a microwave equipment and, more particularly, to a self-checking circuit for accurately measuring electric power of a relevant microwave equipment by compensating for characteristics of each detector changing according to temperature and displaying degrees of the electric power of microwave signals allowing close observance in the microwave equipment, thereby making it easy to check, maintain, and repair the system.
2. Discussion of Related Art
Generally, a microwave equipment uses a wave guide and coaxial line as a signal transmission line. The wave guide is disturbed in its function by change in its form caused by shock from outside or introduction of foreign substances or by change in environment such as pressure and temperature. For the coaxial line, the function may not be done well due to superannuation or breaking of a wire. These may influence other components which are normally operating. In this case, it is difficult to determine with the naked eye what components lose their functions in the overall circuit, so periodical check using a function measuring equipment is needed. Therefore, checking circuits should be installed at every important monitoring point on a signal transmission path of the microwave equipment to check whether each component operates in normal in the system.
FIG. 1 shows an embodiment of a conventional self-checking circuit installed at one of multiple monitoring points on a microwave main signal path. The conventional self-checking circuit comprises: a directional coupler 7 for separating and extracting a portion of a microwave signal passing through the microwave main signal path; a detector 1 for converting the portion of the microwave signal separated and extracted by the directional coupler 7 into a low frequency signal using an envelop detection method; an amplifier 2 for amplifying a signal, which is detected by the detector 1 and has weak electric power, to produce a signal having a predetermined electric power level; a comparing unit 3 for comparing the electric power of a signal amplified by the amplifier 2 with a predetermined value and producing a result value of the comparison; an interface 5 for receiving the result signal from the comparing unit 3 and identifying a location of a checked component; and a display 4 for visibly displaying a signal outputted by the interface 5.
With reference to FIGS. 1 and 2, operation of the conventional circuit having such configuration explained above will now be described in detail.
FIG. 2 shows a detailed configuration of a detecting unit 10 according to the prior art.
The directional coupler 7 is connected to a monitoring point to be checked on the microwave main signal path, and an output signal of the directional coupler 7 is applied to the detection unit 10 consisting of the detector 1, amplifier 2, and comparing unit 3.
In this case, a portion of the microwave signal passing through the monitoring point to be checked on the microwave main signal path is separated and extracted by the directional coupler 7.
The extracted portion of the microwave signal received from the directional coupler 7 is detected through the envelop detection method by the detector 1, thus removing a high frequency portion from the microwave signal and detecting a low frequency signal.
The low frequency signal outputted from the detector 1 has very weak electric power. The amplifier 2 amplifies a level of the low frequency signal up to a predetermined power level and applies a result signal of the amplifier 2 to the comparing unit 3.
The comparing unit 3 compares the level of the signal, which becomes to have sufficient electric power through the amplifier 2, with a reference value which has previously been set therein and applies a result value of the comparing unit 3 to the interface 5 in a processing unit 20.
The interface 5 transmits the result value from the comparing unit 3 to the display 4. The display 4 displays normality or abnormality based upon the result value.
With reference to FIG. 2, the comparing unit 3 which determines normality/abnormality of the monitoring point will now be described in detail.
The comparing unit 3 comprises a comparator 8 and a variable resistor 6.
The variable resistor 6 coupled to one terminal of the comparator 8 is grounded and sets the reference value, or a threshold level. Consequently, a signal which has been amplified by the amplifier 2 and then applied to the other terminal of the comparator 8 is recognized as a signal of higher or lower level than the threshold level set by the variable resistor 6.
However, such electric power measuring circuit of the conventional microwave equipment just outputs "GOOD" or "FAIL" as a result of comparing the electric power of a detected signal from the amplifier 2 with a predetermined value. Change in inner temperature of the microwave equipment results in a change in an output value of the detector since the detector is very sensitive to the temperature. Consequently, abnormality may be displayed even though, actually, the equipment operates in normal.
In this regard, the conventional self-checking circuit of the microwave equipment can detects an error only when a component concerned in the microwave equipment is completely out of order instead of previously detecting and predicting deterioration of the performance of the overall system caused by deterioration of the performance of each component. This makes it difficult to repair or replace a component which may be a major cause that a lifetime of the overall microwave equipment is reduced.
On the other hand, there is a problem in that a good component without malfunction may be replaced.
In addition, since this conventional circuit just determines "GOOD" or "FAIL", a special microwave electric power measuring equipment is required when the system is checked, maintained and repaired to prevent the deterioration of the performance of the system.